1. Field of the Invention
The present invention relates to antennas. More specifically, the present invention relates to electronically scanned antennas.
2. Description of the Related Art
Seekers are used to sense electromagnetic radiation. For certain applications, there is a requirement for at least two seekers. For example, in the missile art, there is a need for an infrared (IR) seeker and a radio frequency (RF) seeker. As both seekers must be mounted in the nose of the missile, one typically at least partially obscures the field of view of the other. The IR seeker not only creates a blind spot for the RF seeker, but also, degrades the field radiation pattern of the antenna thereof.
The situation is exacerbated by the fact that there is a trend toward the use of higher frequency seekers to achieve higher levels of performance in target detection and discrimination. While current RF seekers operate in the X band (8 to 12 GHz), these newer seekers are planned to operate in the Ka band or the W band (27 to 40 GHz). However, a need would remain for the X band capability. Hence, two antennas are required giving rise to the aforementioned problem of occlusion.
Accordingly, there is a need in the art for a system or method for integrating two or more seekers into a single housing in such a manner that neither seeker interferes with the operation of the other.
The need in the art is addressed by the antenna and antenna excitation method of the present invention. The inventive antenna includes an array of radiating elements, each of the elements being mounted at a predetermined substantially transverse angle relative to a longitudinal axis and a circuit for providing an electrical potential between at least two of the elements effective to scan a transmit or a receive beam of electromagnetic energy along an elevation axis at least substantially transverse to the longitudinal axis.
In the illustrative embodiment, the array includes a stack of the planar, parallel, conductive, ring-shaped radiating elements, each of which is filled with ferroelectric bulk material. Space matching material is disposed on the inner and outer periphery of each element.
A second circuit is included in the specific implementation for exciting at least some of the elements to cause the elements to generate a transmit or a receive beam of electromagnetic energy off-axis relative to the longitudinal axis. In the preferred embodiment, the second circuit is a Butler matrix and is effective to cause the beam to scan in azimuth about the longitudinal axis, the azimuthal axis being at least substantially transverse to the longitudinal axis and the elevational axis.